1. Field of the Invention
The present invention relates to a cutter head mounted on a tunnel boring machine, a shield machine, or a vertical shaft excavating machine; a tunnel excavating machine having the cutter head applied thereto; and a cutter replacing method for replacing cutter bits mounted on the cutter head.
2. Description of Related Art
A shield excavating machine, for example, is composed of a cylindrical machine body; a rotationally drivable, disc-shaped cutter head rotatably mounted on a front portion of the machine body; many leading bits and cutter bits attached to the cutter head; many shield jacks mounted behind the cutter head for advancing the machine body, and an erector mounted behind the cutter head for assembling segments to an internal wall surface of an existing tunnel. Thus, when the shield jacks are extended while the cutter head is rotating, the machine body advances under a reaction force arising from excavation which is generated at existing segments. As a result, the leading bits and the cutter bits excavate the ground lying ahead, thereby forming a tunnel.
With such tunnel excavation work, the leading bits mounted on the cutter head scars the surface of the ground lying ahead, facilitating excavation. Then, the cutter bits excavate the ground which has become easy to excavate, and the machine body makes an advancing motion. If an unexpected obstacle, such as a sheet pile, an H-steel pile, or a reinforced concrete pile, is present in the ground ahead during excavation of a tunnel, the leading bits are unable to grind such an obstacle, and their front ends are damaged. Therefore, the customary practice is to replace the leading bits mounted on the cutter head by pile cutting bits, cut and grind the obstacle, such as the concrete pile or wood pile, by the pile cutting bits, and discharge the broken obstacle to the outside together with earth and sand.
A recent tendency toward an increase in the length of a tunnel to be excavated involves wear of leading bits and cutter bits mounted on the cutter head during excavation of the tunnel. Since worn leading bits and cutter bits cause an impairment in ground excavation efficiency, excavation operations must be halted to replace the worn bits. Conventionally, when leading bits and cutter bits are to be replaced, the ground lying ahead is stabilized by injection of a chemical liquid or by freezing. When excavation progresses to the ground-stabilized point, the excavating machine retreats, and muck is removed from inside a chamber of the machine. Then, a worker enters a space located ahead of the cutter head and within the chamber, and replaces the bits.
However, this replacement operation involves the cost of the chemical liquid used to stabilize the ground and is thus uneconomical. Furthermore, the replacement operation is time-consuming and impairs work performance. Moreover, the worker works in a narrow space, such as a space located ahead of the cutter head or a space within the chamber. Such restrictive work conditions increase a burden on the worker.
The present invention has been accomplished to solve the foregoing problems. An object of the invention is to provide a cutter head, a tunnel excavating machine, and a cutter replacing method, which make cutter bit replacement operations easy and quick to perform, thereby lessening burden imposed on workers, and improving safety and excavation work efficiency.
To achieve the above object, a first aspect of the present invention provides a cutter head comprising a rotatably mounted rotor, spokes provided radially on the rotor and each having a plurality of mounting holes provided in a column, a plurality of cutter bits mounted movably to the mounting holes of the spoke and withdrawably into the spoke, fixing means for fixing the cutter bits at positions at which front ends of the cutter bits protrude outward from the spoke, and gate means for closing the mounting hole when the cutter bit is withdrawn.
According to this configuration, the worker performs an operation for replacing the cutter bit at a rear portion of the spoke. This obviates the need to inject a chemical liquid for stabilizing the ground lying ahead, shortens the operating time, and reduces the operating cost. Moreover, the worker need not go out of the machine into a space, such as a space ahead of the cutter head or within a chamber. The burden on the worker decreases, safety can be improved, and the excavation efficiency can be raised. During replacement of the cutter bit, moreover, incursion of muddy water, etc. from the mounting hole can be inhibited by the gate means. Thus, incursion of muddy water, etc. into the spoke can be prevented reliably, and the safety of operation can be fully ensured.
In this case, the cutter bits may be leading bits protruding forward from a front surface portion of the spoke. These bits should desirably be applied when replacing worn leading bits with new ones, or when replacing the leading bits by pile cutting bits which can cut or grind an obstacle such as a concrete pile or a wood pile.
The above-mentioned fixing means may be a fastening bolt for fixing a flange portion formed in a rear end portion of the cutter bit to the spoke. To the flange portion, a pull-out bolt may be screwed, the pull-out bolt being rotated during loosening of the fastening bolt to have a front end thereof pressed against the spoke, thereby withdrawing the cutter bit from the mounting hole. Therefore, fastening and loosening operations for the cutter bit are facilitated, and the withdrawal of the cutter bit becomes easy.
The above-mentioned gate means may be a valve plate which has a through-hole in alignment with the mounting hole and allowing passage of the cutter bit, and which, when the cutter bit is withdrawn from the mounting hole, moves while retaining the cutter bit, thereby closing the mounting hole. Thus, a gate need not be provided separately, so that the structure can be simplified, and the sites of sealing are decreased in number, thus improving the sealability.
A plurality of the valve plates may be rotatably supported on a back side of the spoke. According to this arrangement, the cutter bits can be replaced per block. If one of the cutter bits touches an obstacle present in the ground lying ahead, thus bends, and becomes unwithdrawable from the mounting hole, only the affected block is unreplaceable. Hence, a decrease in the excavation efficiency, or impossibility of excavation, due to the irreplaceability of many leading bits, can be prevented. Thus, reliability can be increased.
A plurality of through-holes may be provided parallel in the valve plate, and a positioning pin for locating the valve plate at a predetermined position may be provided. Thus, a reaction force responsive to excavation that acts on the cutter bit during an excavation operation can be accepted reliably.
The positioning pin may be moved rearward to protrude, and the positioning pin may be pushed sideways to make the valve plate turnable. Thus, a turning jig for the valve plate need not be provided separately, and the valve plate can be turned easily.
The valve plate may be supported inside the spoke movably along a longitudinal direction of the spoke so that the valve plate can hold the plurality of cutter bits. Thus, a single movement of the valve plate enables many cutter bits to be replaced. The replacing operation can be performed easily and quickly to improve and the work efficiency.
The valve plate may be movable by extension and contraction motions of a jack. Thus, a turning device for the valve plate need not be provided separately, and the valve plate can be turned easily to improve the work efficiency.
A second aspect of the invention is a tunnel excavating machine comprising a cylindrical machine body, propelling jacks for advancing the machine body, a cutter head rotationally drivably mounted on a front portion of the machine body, spokes provided radially on the cutter head and each having a plurality of mounting holes provided in a column, a plurality of cutter bits mounted movably to the mounting holes of the spoke and withdrawably into the spoke, fixing means for fixing the cutter bits at positions at which front ends of the cutter bits protrude outward from the spoke, and gate means for closing the mounting hole when the cutter bit is withdrawn.
According to this configuration, the worker performs an operation for replacing the cutter bit at a rear portion of the spoke. This obviates the need to inject a chemical liquid for stabilizing the ground lying ahead, shortens the operating time, and reduces the operating cost. Moreover, the worker need not go out of the machine into a space, such as a space ahead of the cutter head or within a chamber. The burden on the worker decreases, safety can be improved, and the excavating work efficiency can be increased. During replacement of the cutter bit, moreover, incursion of muddy water, etc. from the mounting hole can be inhibited by the gate means. Thus, incursion of muddy water, etc. into the spoke can be prevented reliably, and the safety of operation can be fully ensured.
A replacement room nearly at an atmospheric pressure, where a worker can enter from the machine body and replace the cutter bit, may be provided in a rear portion of the spoke. Since the worker performs cutter replacing work in this replacement room, the worker need not go out of the machine into a space, such as a space ahead of the cutter head or within a chamber. The burden on the worker decreases, safety can be improved, and the excavating work efficiency can be increased.
The above-mentioned gate means may be a valve plate which has a through-hole in alignment with the mounting hole and allowing passage of the cutter bit, and which, when the cutter bit is withdrawn from the mounting hole, moves while retaining the cutter bit, thereby closing the mounting hole. Thus, a gate need not be provided separately, so that the structure can be simplified, and the sites of sealing are decreased in number, thus improving the sealability.
A third aspect of the invention is a cutter replacing method comprising moving a cutter bit rearward, the cutter bit being mounted in such a manner as to protrude from a front face of a cutter head, then turning a valve plate having the cutter bit supported thereon so that a cutter bit mounting hole formed in the cutter head is closed with the valve plate, replacing the cutter bit by other cutter bit in this state, then turning the valve plate again to bring the new cutter bit and the cutter bit mounting hole into alignment, and then moving the cutter bit forward and fixing the cutter bit.
According to this method, the worker performs an operation for replacing the cutter bit at a rear portion of the spoke. This obviates the need for the worker to go out of the machine into, for example, a space ahead of the cutter head or within the chamber. The burden on the worker decreases, and safety can be improved. During replacement of the cutter bit, the mounting hole is closed with the valve plate. Thus, incursion of muddy water, etc. into the interior can be inhibited. Consequently, incursion of muddy water, etc. into the spoke can be prevented reliably, and the safety of operation can be fully ensured.